Wire insulation testing apparatus with means indicating insulation faults per predetermined incremental length

ABSTRACT

Test apparatus is disclosed which provides continuous nondestructive tests for faults in insulation coatings on wire. Means are provided for counting detected faults and actuating an alarm when the fault rate exceeds an undesired limit for any predetermined incremental length of wire. Switch means are provided which automatically adjust measuring sensitivity to correspond with the switch selected D-C test voltage applied to the insulation under test.

United States Patent 1191 Pendleton et al.

[11] 3,823,370 [451 July 9,1974

WIRE INSULATION TESTING APPARATUS [54] 4/1961 Fountain 324/54 WITH MEANS INDICATING INSULATION 2,999,168 9/1961 Henry 323/1 15 X FAULTS PER PREDETERNHNED 3,196,072 7/1965 Wirtz 73/159 X 3,217,246 11/1965 Kallet et al. 324/54 INCREMENTAL LENGTH 3,281,675 10/1966 Shillington.... 324/54 [75] Inventors: Wesley William Pendleton; Robert g a ct a a son e a 523: 2 3 2? both of 3,413,541 ll/l968 Swim et al. 324 54 g 3,417,265 12/1968 Lee 307/247 Assignee: Anaconda Wire & Cable Company, 3,491,290 1970 Peschel 324/54 New York, Y 3,536,994 /1970 Johnson 324/34 TA 3,619,578 11/1971 George 235/92 DN X [22] 1971 FOREIGN PATENTS OR APPLICATIONS 1 1 PP 170,307 1,066,472 4/1967 Great Britain 324/34 TA Related US. Application Data 1 [63] Continuation of Ser. No. 876,968, Nov. 14, 1969, Pnmay Exammer -Gerard R' Strecker abandoned, ABSTRACT 52 Us. c1. 324/54 Test pp p is disclosed which p s continupus [51] Int. Cl G0lr 31/12 non'destructlve tests for faults msulatlo" coatmgs [58] Field f Seal-chm" 4 5 34 35 92 on wire. Means are provided for counting detected 1 35 200; 73 159 faults and actuatmg an alarm when the fault rate exceeds an undesired limit for any predetermined incre- [56] References Cited mental length of wire. Switch means are provided UNn-ED STATES PATENTS which automatically adjust measuring sensitivity to 5 2 D correspond with the switch selected D-C test voltage 5232 38) 23 applied to the insulation under test.

2:902:674 9/1959 Billings et a1... 307/247 1 Claim, 2 Drawing Figures 2,942,248 6/1960 Huggins 324/54 X u TEST WIRE 1e i f [4 77 looft/rev l5 VOLTAGE I9 75 %SELECTOR 37 2143 g 5 A 27s 21 27A 29 LOCK UP CURRENT AIL el ii AND INVERTEQ PULSE 2o AMPLIFIER DETECTOR GATE sEm RAroR WJP'G 210 36 I Q g n l I82 (Test) lg Bl S80 40A 40 1 1 "\ANVV 2 1 i5 5; -ALARM COUNTER I 5 1 ON DRIVER V 5 I AMPLIFIER I 601 I 5(3 f i I FF FF I l -l l MANUAL RESET PATENIEDJIIL 9:914 3.8231370 sum 2 or 2 (4500 V.) V i- H .6 mg-1 m uddiiipncl 1 S I ,J test umtsf I H.V. 2500 SELECTOR SWITCH zooov. off

IOOOV.

IO M

750V. IS S IOM 0575M 6 M to Fault 350V Detector 0 off SENSITIVITY SELECTOR SWITCH 0.90M

1 INVENTORS WESLEY WILLIAM PENDLETON ROBERT C. THOMPSON WIRE INSULATION TESTING APPARATUS WITH MEANS INDICATING INSULATION FAULTS PER PREDETERMINED INCREMENTAL LENGTH CROSS REFERENCE TO RELATED APPLICATION This is a continuation of my application Ser. No. 876,968, filed Nov. 14, 1969, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to apparatus for electrically testing insulation coatings on wire to detect undesired faults or discontinuities. More particularly, it relates to apparatus for detecting faults in enamel insulation coatings on relatively small magnet wire while the wire is moving at relatively high speeds. Such fault tests are advantageously made immediately after the wire has passed through the enamel curing oven immediately prior to being wound on spools.

Manufacturing standards have been established setting a maximum fault-rate limit of three, five and 10 faults per I feet for triple, heavy and single film insulation coatings, respectively. To have assurance that these industry standards are complied with, his essential that all manufacturing production of such coated wire be continuously tested. It is desirable of course to make the continuity tests as rapidly as possible; on the other hand, as a practical matter it is difficult to sense and record extremely short duration fault currents generated by small pinhole defects traveling at high speeds past the test instrument. Reliable testing is further complicated by the fact that measuring sensitivity must be increased as a function of insulation thickness and, at the same time, current flow through the insulation voids must be limited to prevent insulation destruction throughout the range of DC high voltages that are utilized.

One of the time consuming problems encountered with the use of prior art insulation testing devices is that of counting the detected faults (normally recorded on a chart recorder) in order to evaluate production quality based on fault-rate industry standards.

It is a principal object of the present invention to provide a reliable insulation continuity tester which can be quickly adjusted to measure faults in a wide range of coating thickness, and at the same time automatically actuate an alarm indicator when the fault rate exceeds a preselected limit.

DESCRIPTION OF THE INVENTION The present invention provides a continuous, highspeed, D-C type wire insulation tester with means for adjusting applied test voltage over a wide range of values and at the same time maintaining both a desired level of instrument measuring sensitivity and a limited maximum value of power through the insulation faults to prevent insulation damage. A

In a preferrred embodiment of the invention, circuit means are provided for converting both short duration pinhole defects and the longer bare-wire defects into uniform pulse widths which can be reliably recorded on inexpensive slow-response recorders. A fault-rate counter is provided with means to actuate an alarm indicator whenever the number of counted faults per incremental length equals or exceeds the desired standard.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a block diagram showing a preferred embodiment of the invention; and

FIG. 2 is a circuit diagram showing the test highvoltage and sensitivity selector switches.

Referring to FIG. 1, there is shown high voltage selector switch with high-voltage input terminal 11, and variable output test voltage terminal 12 connected to grooved contact wheel 14 through current limiting resistor 13. A predetermined value of DC high voltage selected by variable voltage selector 15 is applied to the test wire 16 (the conductor core of which is grounded as shown) after enamel insulation has been applied. Current flow from wheel 14 through faults in the insulation coating on 16 produce voltage pulses across current sensing resistor 19 which are amplified by current amplifier 20 to a level which is suitable to actuate an adjustable threshold voltage level detector 21 with current pulses produced by the highest resistance pinhole faults desired to be detected (eg. 80 megohm). Amplifier 20 preferably comprises a plurality of cascaded emitter followers which provide desired high input impedance and a stable current gain characteristic.

. Voltage level detector 21 may comprise a differential amplifier one input of which is supplied'with varying amplitude fault current pulses 25 and the other input of which is connected to an adjustable threshold level control 26. Level control 26 is set at a desired value to eliminate passage of all fault current pulses below a predetermined amplitude 25A. Current pulses 27 produced by faults exceeding predetermined level 25A are supplied to one input 28 of AND-gate 30 and pulses from pulse generator 31 are supplied to the other input 29. Pulses from 31 serve to close gate 30 at, for example, a one cycle per second rate and thereby provide a continuous fault count of one per second for the longer duration bare-wire faults exemplified by pulse 27A. The on-off duty cycle of the 1 Hz pulses is preferably large (i.e., 20:1) so that gate 30 is maintained in the open position to pass short duration pinhole fault pulses 27B 95 percent of the time. Output pulses from 30 are supplied to a one-shot pulse generator 35 and clamp auto-lock-up 37 via polarity inverter 36. All fault pulses, those generated by small pinholes as well as the one cycle per second pulses generated by bare-wire defects, are translatedby generator 35 to constant width fault-count pulses having sufficient time duration (e.g. 25 msec.) to operate inexpensive solenoid actuated recorder 38 and counter 39 having slow response times. Clamp 37 is advantageously employed to maintain a rest or retention time 40A of approximately 25 msec. between pulses to pennit recovery of the electromechanical counter 39. Clamp 37 thereby prevents any pinhole fault signals from being supplied to the counter 39 via driver amplifier until an adequate recovery time has elapsed after each fault count signal.

In accordance with a principal feature of the'invention, fault signals from 45 are also supplied to a digital count-down or fault-rate counter comprising four serially connected flip-flops 51, 53, and operatively connected to provide fault-rate alarm control signals of three, five or 10 per 100 feet of wire tothe correspondingly indicated terminals of selector switch 70. Countdown 50 is automatically reset to zero fault count by the closing of reset switch once every revolution of cam wheel 76 driven at the rate of one revolution per lOO feet of wire by 14 through reduction gear 77.

Switch 70 may be set to the desired NEMA (National Electrical Manufacturers Association) limit of three, five or 10 faults per lOO feet as required for testing of 5 triple, heavy or single build insulation and the operators alarm indicator 80 is actuated by the fault alarm signal supplied by lead 81 to reset lock-on circuit 82 which holds the alarm (visual and/or audible) in the actuated or on position until the operator closes manual reset switch 85.

In actual operation, it is desirable to have a relatively wide range of D-C test voltages (e.g., 350V. to 3,000V.) available on a switch selected basis in order to facilitate'testing of varying insulation film thicknesses (e.g., 0.0002 to 0.0042 inches). At the same time, fault resistance sensitivity changes over a range of from about megohms for thin film coatings to 90 megohms for thick insulation coatings. In accordance with one aspect of the present invention, ganged switch means 158 and 198 are provided as shown in FIG. 2 which simultaneously and automatically modify fault sensitivity to a level appropriate for the test voltage selected by for a given insulation thickness so that the fault current level is maintained substantially constant (e.g. 3 megohms/100 volts applied).

Insulation testers proposed in the prior art have utilized a separate high-voltage power supply to energize each test unit which adds considerably to the overall cost of a multi-unit testing installation. in accordance with one aspect of the present invention, a single regulated highvoltagesupply is utilized to simultaneously energize a plurality of operating insulation testers as indicated in FIG. 2. To assure non-destructive testing, current is limited by resistor 13 so that the maximum power supplied to a fault does not exceed 0.15 watts (i.e., product of open circuit test voltage and short circuit current). It has been found that this level is sufficiently high to provide a reliable fault current signal free of cross-talk between plural test instruments operated from a single regulated supply, and at the same time low enough to avoid damage to the wire insulation. Typical parameters are as follows:

Range of Fifi? fiuiid AWG Range 11c. Sens.

Inches Single Heavy Triple Voltage Meg.

00002-00005 40-34 350 10.5 00006-00008 33-30 40-38 500 15.0 0,000l'i-0i00l l 29-2l 37-33 40-38 750 22.5 0.00l2-(L00l6 20-]4 32-27 37-33 i000 30.0 00017-00029 26-16 32-19 i500 45.0 00030-0003 3 l5-8 l 8-10 2000 600 00034-00037 7-4 9-6 2500 750 amiss-0.0042 5 3 3 Q00 90.0

It will be appreciated that various changes may be made in the above-described preferred embodiment of the invention. For example, various types of counters may be employed as fault rate counters such as the well known ring, step analog, electromechanical and the like. Similarly, an adjustable timer controlled switch may be utilized in place of the illustrated gear and cam actuated microswitch to periodically reset the faultrate counter 50.

We claim: 7 V H g 1. Apparatus for continuously testing continuity of the insulation coating on a moving insulated wire conductor, said means comprising 7 a. contact means for applying a D-C high voltage test potential between the exterior surface of insulation coating and the interior conductor; b. means for sensing and amplifying pulses of current flowing through faults in said insulation coating;

and W N c. fault-rate counter means for counting the number of fault current pulses for each successive predetermined incremental length of insulated wire, said fault-rate counter means including a counter for accumulating a count corresponding to the number of such fault current pulses, means including a cam rotated by the passage of the moving insulated wire for resetting said counter to zero after the passage of each successive predetermined incremental length of insulated wire, and means responsive to said counter for indicating the accumulation of a count greater than a predetermined maximum value therein, wherein'said sensing and amplifying means includes a current sensing impedance in circuit with the contact means and a voltage level detector responsive thereto for selecting and amplifying fault current pulses having amplitudes greater than a predetermined level corresponding to the maximum fault impedance to be sensed for producing fault-count signals;

said fault-rate counter means including a pulse generator for generating a periodic switch control signal, an AND-gate for producing an output responsive to the coincidence of signals from the voltage level detector and the pulse generator, and circuit means responsive to the output ofthe AND-gate for extending the time duration of each output signal therefrom, said output signals being connected to increment said counter; said indicating means constituting an alarm and said fault-rate counter including a control switch for selecting a particular number of .faults necessary to actuate the alarm.

0 UNITED STATES PATENT OFFICE {CERTIFICATE OF CORRECTION 3,823,370 Dated July 9, 1974 Patent No. I

I WESLEY WILLIAM PENDLETON et a1 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 43, 0.0006 0.0003" should read 0, 0006 0.0007

signed 5nd aie thie 31 a d5 of December 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHAL L DANN A ttesting Officer Commissioner of Patents uscoMM-oc' scan-Pee k ",5. GQVIRNMINTfIINTING OFFICE 31.. O-SIi-Sll.

FORM PO-1050(10-\3) 

1. Apparatus for continuously testing continuity of the insulation coating on a moving insulated wire conductor, said means comprising a. contact means for applying a D-C high voltage test potential between the exterior surface of insulation coating and the interiOr conductor; b. means for sensing and amplifying pulses of current flowing through faults in said insulation coating; and c. fault-rate counter means for counting the number of fault current pulses for each successive predetermined incremental length of insulated wire, said fault-rate counter means including a counter for accumulating a count corresponding to the number of such fault current pulses, means including a cam rotated by the passage of the moving insulated wire for resetting said counter to zero after the passage of each successive predetermined incremental length of insulated wire, and means responsive to said counter for indicating the accumulation of a count greater than a predetermined maximum value therein, wherein said sensing and amplifying means includes a current sensing impedance in circuit with the contact means and a voltage level detector responsive thereto for selecting and amplifying fault current pulses having amplitudes greater than a predetermined level corresponding to the maximum fault impedance to be sensed for producing fault-count signals; said fault-rate counter means including a pulse generator for generating a periodic switch control signal, an AND-gate for producing an output responsive to the coincidence of signals from the voltage level detector and the pulse generator, and circuit means responsive to the output of the AND-gate for extending the time duration of each output signal therefrom, said output signals being connected to increment said counter; said indicating means constituting an alarm and said fault-rate counter including a control switch for selecting a particular number of faults necessary to actuate the alarm. 